Manual hydraulic dock board hold down arrangement

ABSTRACT

A hydraulic hold down locking cylinder is disclosed by replacing mechanical lock arrangements commonly used on less expensive dock boards. This arrangement provides superior performance, reliability, and lower maintenance. In the preferred form all components are provided in a cylindrical casing which is mounted as a variable length locking link in the dock board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/161,253, filed Dec. 3, 1993, which issued as U.S. Pat. No. 5,551,113.

FIELD OF THE INVENTION

The present invention relates to a manual lock arrangement for amechanical dock board and, in particular relates to a manual hydrauliclock arrangement.

BACKGROUND OF THE INVENTION

There are many dock board systems which have a mechanical arrangementfor raising and lowering thereof and generally include a mechanical lockarrangement for locking the dock board in a particular position.Unfortunately, the loads exerted on the dock boards, and hence on themechanical arrangements, change and, in particular, change due to thevariable load or support the trailer bed exerts on the dock board as thetrailer is being loaded or unloaded.

Problems occur when a trailer is unloaded in that the suspension of thetrailer tends to raise the bed of the trailer and the dock board. Themechanical lock arrangement of the locked dock board tries to opposethis upward force and movement. This can result in very high loads onthe dock board and causes high wear and deterioration of the mechanicallock. These lock mechanisms also become progressively more difficult torelease as the load on the dock board increases and can lead to operatorinjury. The release problem is more acute if high upward loads arepresent, such as when a trailer is unloaded.

The unloading or loading of trailers typically involves a fork lifttruck or other device which weighs 3000 to 5000 lbs. or more without theweight of the product. This causes the dock board and trailer to go downwhen the fork lift truck crosses the dock board, and the dock board andtrailer should go up when the fork lift truck crosses over the dockboard from the trailer. Thus, the forces exerted on the dock board varywidely during use.

Many mechanical dock board systems, as opposed to powered hydraulicallycontrolled dock boards (having pumps and electrically controlledvalves), are used in factories as they are generally less expensive and,typically, the owner of the building is not responsible for maintenanceof the dock boards. This responsibility is typically the responsibilityof the tenant renting the premises.

There remains a need for a simple arrangement for effectively lockingthe manual mechanical type dock boards in various positions whileaccommodating the variable forces thereon.

The present invention is directed to nonpowered, manual mechanical typedock boards and is not directed to powered hydraulic dock boards whichare many times more expensive and require power at the dock board.

SUMMARY OF THE INVENTION

According to the present invention, the mechanical lock of a loadingdock is replaced with a hydraulic locking arrangement. The hydrauliclocking arrangement allows the dock plate to move downwardly when anyforce is applied to the dock plate which is of a sufficient magnitude toovercome the spring bias urging the dock plate to a raised position. Thehydraulic locking arrangement locks the dock plate against upwardmovement until a predetermined pressure is exceeded. The lockingcylinder comprises a moveable piston, a high pressure hydraulic fluidcircuit acting on one side of the piston for opposing movement of thepiston in a direction to raise said dock plate, a hydraulic fluidreservoir, a high pressure check valve arrangement connecting the highpressure hydraulic fluid circuit with the reservoir. The high pressurecheck valve arrangement opens to the reservoir and when a predeterminedpressure is exceeded, the check valve opens and allows some of thehydraulic fluid to be returned to the reservoir. This typically occurswhen the dock board is urged upwardly by a trailer bed which is beingunloaded. Once the pressure has been relieved, the check valve closesand the hydraulic locking cylinder again locks the dock board in place.The hydraulic locking cylinder includes a low pressure check valvearrangement for accommodating movement of the piston within the cylinderin response to lowering of the dock board. In this way, any force of amagnitude exceeding the spring pressure urging the dock board to pivotdownwardly, causes the dock board to move downwardly in a controlledmanner due to the hydraulic fluid passing through the low pressure checkvalve. Once the dock board assumes new working positions, the cylinderis essentially locked until the high pressure check valve pressure isexceeded or the dock board moves downwardly. The hydraulic fluid withinthe circuit will be at different pressures depending primarily on thevariation in an upward forces exerted on the dock board. The hydrauliclocking cylinder also includes a manual release means for the highpressure check valve arrangement to allow the cylinder to accommodatecontrolled movement of the dock platform to the raised position underthe influence of the spring bias. This raised position is typically usedas a standby position until such time as a trailer bed has beenpositioned in front of the dock board. The user can then walk on to thedock plate, overcome the spring bias of the dock board and the dockplate will move downwardly until it bottoms out on the bed of thetrailer. The dock plate is locked against upward movement by thehydraulic locking cylinder (i.e. the trapped hydraulic fluid in thecircuit between the piston and the high pressure check valve).

It has been found that the locking arrangement of the invention canreplace the troublesome mechanical locking arrangement found with manymechanical dock boards and provide superior performance.

The dock board also "floats " or constantly adjusts during use thereofto accommodate the varying loads exerted thereon during loading orunloading of a trailer or vehicles.

These advantages are achieved in a manual nonpowered dock board in aneffective, reliable manner and provide an extremely effectivealternative to manual mechanical hold down mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawingswherein:

FIG. 1 is a perspective view of a mechanical dock board with thehydraulic cylinder locking arrangement;

FIG. 2 is a side view of a dock board located in a pit and co-operatingwith the bed of a trailer;

FIG. 3 is a sectional view of the hydraulic locking cylinder showingcertain aspects of the hydraulic locking cylinder;

FIG. 4 is a sectional view showing the locking cylinder in a stationaryposition;

FIG. 5 is a sectional view showing the locking cylinder when a force isbeing exerted on the cylinder rod in a retraction direction (downwardmovement of the dock board); and

FIG. 6 is a sectional view of a further embodiment having an endreservoir.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One example of an adjustable mechanical loading dock 2 is shown inFIG. 1. The loading dock includes a frame 4, a pivoting dock board 6 anda mechanical linkage generally shown as 8 for controlling movement ofthe pivoting dock board 6. A spring bias arrangement 10 urges the dockboard to a raised position as shown in FIG. 1. The spring biasarrangement 10 can be set such that a operator can stand on the dockboard 6 and cause the dock board to move downwardly.

As shown in FIG. 2, the dock board 6 is moved downwardly until it comesinto contact with the bed of a trailer generally shown as 22. If theoperator's weight is removed, the spring bias arrangement, if unopposed,would return the dock board to a raised position. To overcome this, thehydraulic locking cylinder 12 opposes any upward movement of the dockboard 6. As will be explained in greater detail with respect to FIGS. 3,4 and 5, the hydraulic locking cylinder has a release mechanism shouldthe pressure exerted on the dock board in an upward direction exceed apredetermined force. It is this upward force which has been the sourceof significant problems with respect to mechanical locking arrangementsresulting in these locking arrangements typically failing or requiring ahigh degree of maintenance due to excessive wear.

The upward force, generally indicated as 19 in FIG. 2, is caused by atrailer generally shown as 20 being unloaded with the dock board incontact with the bed 22 of the trailer. As the trailer is unloaded, thesuspension of the trailer tends to raise the bed 22 from an initiallevel generally indicated as 24 to a raised level indicated as 26. Thisprovides a strong load on the dock board urging it to move in the upwarddirection. With the present hydraulic arrangement, when the upward forceexceeds a predetermined limit (preferably about 1000 psi), a highpressure check valve is opened and allows the dock board to moveupwardly and assume a new locked position. Thus, the hydraulic lockingcylinder arrangement allows the dock board to generally move in acontrolled manner downwardly and provides a progressive lock againstupward movement.

Loading or unloading of a trailer typically requires a fork lift truckor other heavy device to cross the dock board. This results in highdownward loads when the fork lift truck is on the dock board, which isopposed by the suspension of the trailer, however, the dock board andtrailer move downwardly. As the fork lift truck leaves a trailer andleaves the dock board, the trailer exerts a high upward load on the dockboard. Typically, this load is of sufficient magnitude to exceed thepressure limit of the high pressure check valve, such that the dockboard moves upwardly, relieving the force.

In this way, the dock board moves down and then up or "floats " toaccommodate the actual forces encountered. This results in a dock boardwhich automatically adjusts to maintain the forces exerted thereon witha satisfactory operating range.

Details of the hydraulic locking cylinder are shown in FIGS. 3, 4 and 5.The hydraulic lock cylinder 12 includes a cylinder casing 30 having anattachment lug generally shown as 31 for securement to the frame of theloading dock. A cylinder rod 32 extends from the cylinder casing and isattached to the pivoting dock board. Within the cylinder casing, thecylinder rod has a piston head 34 which has been drilled to define theport generally indicated as 35. This port is closed by a low pressurecheck valve generally indicated as 56. The cylinder is closed by capmember 38 and a high pressure seal 39 is provided between the cylinderrod 32 and the cap 38.

The cylinder case below the piston head 34 defines a variable volumehydraulic fluid reservoir 44. This reservoir 44 receives any highpressure hydraulic fluid which passes through the high pressure checkvalve 52. This high pressure check valve can be opened by application ofthe manual release 54 or when the locking hydraulic fluid pressureexceeds a predetermined limit which effectively opens the check valve 52(typically about 1000 to 1200 psi). The piston head 34 slides within thecylinder 36.

The cylinder 36 is open at the bottom and it can be seen that thereservoir 44 is in cylinder 36 below the piston head 34 and in the spaceabove and below the cylinder 36. The reservoir 44 is connected to theair vent 60 at the one end of the locking cylinder and is generally at ahigh location. Any air entrapped in the hydraulic fluid contained withinthe reservoir will find its way to the vent 60 and effectively beeliminated from the hydraulic fluid. Note, that the high pressure fluidwhich passes through the high pressure check valve 52, enters thereservoir at a low position and any air or gas entrapped in the fluidwill find its way to the vent 60 and thereby be eliminated. Entrappedair or gas adversely effects the operation of the cylinder.

The hydraulic locking cylinder provides a hydraulic lock againstmovement of the rod 32 in the direction generally indicated as 37 inFIG. 3. A high pressure hydraulic fluid circuit 50 is defined betweenthe piston head 34, the portion of the cylinder 36 above the piston headand through a port arrangement generally shown as 51 in the upper partof the cylinder casing 30. The port or conduit 51 is connected to thehydraulic high pressure check valve 52. Should a trailer bed exert anupward force on the dock board, this force is initially opposed by thehigh pressure hydraulic fluid located within the high pressure circuit50. Should the force exceed the pressure limit of the high pressurecheck valve 52, a small amount of hydraulic fluid passes through thecheck valve and enters the reservoir. Thus, the rod 32 can moveoutwardly or in an extending direction indicated by arrow 37 should thehydraulic pressure exceed the opening pressure of the high pressurecheck valve 52. Any air or gas entrapped in the hydraulic fluid passesthrough the check valve and will move upwardly passed the upper edge ofthe cylinder 36 and pass out of the hydraulic locking cylinder throughthe vent 60.

FIG. 5 shows a force 53 urging the piston rod 32 in a retractiondirection and this force is generally unopposed by the cylinder. Thisaction accommodates downward movement of the dock board, such as wouldoccur when a fork lift truck is entering a trailer. The lower pressurecheck valve 56 is opened (typically at a very low pressure) andhydraulic fluid within the reservoir 44 passes through the port 35provided in the piston head 34 and enters what was previously the highpressure circuit 50 which is now not under pressure. This is the actionof the cylinder when a downward force is exerted on the dock board whichis of a magnitude to overcome the spring bias of the dock board. Thus,the dock board moves under a controlled resistance downwardly ashydraulic fluid flows from the reservoir 44 into the high pressurecircuit 50 although at this point in time, the high pressure circuit 50is under no pressure.

The hydraulic cylinder as shown in FIG. 4 shows both the high pressurecheck valve 52 and low pressure check valve 56 closed. It can beappreciated that pressure within the high pressure circuit 50 will alsoserve to maintain the low pressure check valve 56 closed when there is apressure in the high pressure circuit which exceeds pressure of thereservoir.

As can be appreciated from the above description, the dock board floatsin position, due to the automatic operation of the dock valves, andassumes a position within a satisfactory, predetermined operating range.

The seals 46 provided between the piston rod 32 and the cylinder cap 38stops air from entering or hydraulic fluid from leaving the highpressure circuit 50.

The purpose of the manual release 54 is to allow the operator to causethe dock board to move to the raised position such as would be the casewhen a trailer is about to leave the loading dock. In this case, themanual release 54 is actuated and as there should be no force on thepivoting dock board 6 other than its own weight and the spring bias, itwill move upwardly under the influence of the spring bias 10 to theraised position generally shown in FIG. 1. The dock board is thenpositioned to allow an operator to lower the dock board once a trailerhas been appropriately located. The dock board automatically adjusts forlowering of the trailer bed such as when the trailer is being loaded asthe cylinder essentially allows controlled movement of the dock boarddownwardly. The hydraulic locking cylinder also allows for upwardmovement of the dock board should a force be exerted on the dock boardwhich exceeds the pressure limits of the high pressure check valve 52.This arrangement provides a very reliable, convenient solution forallowing the conversion of a mechanical loading dock to a mechanicalloading dock having an adjustable hydraulic lock.

This arrangement also defines a loop pumping circuit for the hydraulicfluid and allows any entrapped air or gas to be removed therefrom. Inaddition, all components are located within the cylinder structure whichis mounted in the dock board as a variable length locking link.

A manual release mechanism can include a lever arrangement or anelectrical arrangement (typically including a solenoid). The manualrelease is shown as 100 in FIGS. 1 and 3. The lever arrangement can bepivotally secured to the cylinder and provide a mechanical advantage foropening of the check valve. This mechanism is typically accessible atthe rear of the dock board at the upper surface thereof.

An alternate structure is shown in FIG. 6 and differs from the structureof FIGS. 3 and 4, in that a reservoir extension 70 has been added andthe vent 60 has been removed. The reservoir extension is connected tothe variable volume hydraulic fluid circuit 44 by fluid passages 72.Excess hydraulic fluid is forced into the reservoir extension and avolume of air under low positive pressure maintains fluid circuit 44flooded with hydraulic fluid. The intake breather valve 76 operates totake in air if a certain negative pressure (preferably 25 psi) in thereservoir extension. Release breather valve 78 operates to releasepressure at about 25 psi. Each of these valves maintains the hydraulicfluid within the cylinder during shipping and minimizes leakage inshipping and allows the unit to be shipped in a condition ready forinstallation.

The reservoir is sealed by the two valves and therefore, can be shippedwithout leakage. At the time of installation, the unit is already filledand only needs to be installed. The dock board, after installation, iscycled several times during which either or both vents may operate dueto the pressure conditions. Any air trapped in the fluid circuitaccumulates in the reservoir. It has been found that the valves remaingenerally closed after the initial set up, and thus, the fluid circuitis effectively sealed thereby reducing contamination by drawing in airand dirt which can occur in the open system of FIGS. 3 through 5. Asdescribed above, the valved reservoir accommodates necessary changes inoperating the system and effectively closes the hydraulic circuit duringshipping or storage. At the time of manufacture, the unit isappropriately filled with the proper amount of hydraulic fluid and istested. Satisfactory operation at this time strongly indicates the unitwill properly function when finally installed.

The hydraulic locking arrangement, which does not require a separatepower source, has been described with respect to the preferredembodiment where the reservoir and check valves and fluid circuit areall incorporated in a cylinder for mounting directly in the dock boardand operable at various angles generally from horizontal to about a 60degrees. This arrangement is preferred as it simplifies installation andis believed to reduce potential maintenance problems as all componentsare protected and move as a unit. It is possible to simplify thecylinder and provide a separate and distinct reservoir appropriatelyconnected which operates in the manner described and as such is withinthe scope of the present invention.

The present invention also improves the operation of the manualmechanical dock board by providing an automatic adjusting or "floating "dock board which responds to reduced what would otherwise be damagingforces.

Although preferred embodiments of the invention have been describedherein in detail, it would be understood by those of skill in the art,that variations may be made thereto without departing from the spirit ofthe invention and the scope of the appending claims.

What is claimed is:
 1. Hydraulic locking arrangement for a loading dockhaving a pivotally mounted dock plate, said hydraulic lockingarrangement controlling movement of said dock plate from a raisedposition to a lower trailer loading or unloading position, saidhydraulic locking arrangement locking said dock plate against upwardmovement unless a predetermined pressure is exceeded, said hydrauliclocking arrangement comprisinga cylinder, a piston moveable within saidcylinder, a closable hydraulic fluid circuit acting on one side of saidpiston, said closable hydraulic fluid circuit when closed opposing anyforces urging movement of said piston in a direction to raise said dockplate and results in an increase of the hydraulic fluid pressure of saidclosable hydraulic fluid circuit, a hydraulic fluid reservoir, a highpressure check valve arrangement connecting said hydraulic fluid circuitwith said reservoir, a low pressure check valve for accommodatingretraction of said piston and supply of hydraulic fluid from saidreservoir into said fluid circuit, and release means for opening saidfluid circuit and accommodating movement of said piston as said dockplatform is moved to the raised position; said high pressure check valvearrangement opening to said reservoir when a predetermined pressure isexceeded in said hydraulic fluid circuit caused by said dock board beingforced upwardly and automatically closing when the pressure is withinacceptable operating pressure range and wherein said reservoir includesan air valve arrangement which regulates and limits the exchange of airbetween the reservoir and atmosphere.
 2. Hydraulic locking arrangementas claimed in claim 1 wherein said high pressure check valve remainsclosed when acted on by a spring bias force on said dock platform urgingit to an upward position and automatically opens at a higher pressure toavoid forces on said dock board which can damage the operation thereof.3. Hydraulic locking arrangement as claimed in claim 1 wherein saidfluid circuit forms a loop with said reservoir and said high pressurecheck valve is located at a position remote said piston and opens intosaid reservoir and said low pressure check valve is closely associatedwith said piston, and wherein said air valve arrangement effectivelyseals said fluid circuit from atmosphere thereby reducing contaminationof the hydraulic fluid.
 4. Hydraulic locking arrangement as claimed inclaim 3 wherein said low pressure check valve opens at a pressure lessthan about 20 psi.
 5. Hydraulic locking arrangement as claimed in claim3 wherein said low pressure check valve opens at a pressure betweenabout 2 psi and 20 psi.
 6. Hydraulic locking arrangement as claimed inclaim 3 wherein said high pressure check valve opens at a pressure ofabout 1000 psi.
 7. Hydraulic locking arrangement as claimed in claim 1wherein said release means is an actuator which opens said high pressurecheck valve.
 8. Hydraulic locking arrangement as claimed in claim 1wherein said release means is a pivotted lever arrangement which openssaid high pressure check valve.
 9. Hydraulic locking arrangement asclaimed in claim 1 wherein said release means includes a solenoid forreleasing said high pressure check valve.
 10. Hydraulic lockingarrangement as claimed in claim 1 wherein said check valves, saidreservoir, said hydraulic circuit, said piston and said cylinder are alllocated in a common housing.
 11. Hydraulic locking arrangement asclaimed in claim 2 wherein said check valves, said reservoir, saidhydraulic circuit, said piston and said cylinder are all located in acommon housing.
 12. Hydraulic locking arrangement as claimed in claim 3wherein said check valves, said reservoir, said hydraulic circuit, saidpiston and said cylinder are all located in a common housing. 13.Hydraulic locking arrangement as claimed in claim 1 wherein said checkvalves, said reservoir, said hydraulic circuit, said piston and saidcylinder are all located in a common cylindrical housing pivotallysecured in said loading dock.
 14. Hydraulic locking arrangement asclaimed in claim 2 wherein said check valves, said reservoir, saidhydraulic circuit, said piston and said cylinder are all located in acommon cylindrical housing pivotally secured in said loading dock. 15.Hydraulic locking arrangement as claimed in claim 1 including areservoir extension in fluid communication with said reservoir toaccommodate an excess of hydraulic fluid available to said reservoir,said reservoir extension including said air valve arrangement. 16.Hydraulic locking arrangement as claimed in claim 2 including areservoir extension in fluid communication with said reservoir toaccommodate an excess of hydraulic fluid available to said reservoir,said reservoir extension including said air valve arrangement. 17.Hydraulic locking arrangement as claimed in claim 1 wherein said airvalve arrangement has two air pressure valves, one of said pressurevalves operating to vent air in said reservoir at a predeterminedpressure and one of said air pressure valves operating to allow air intosaid reservoir at a predetermined negative pressure in said reservoir.18. Hydraulic locking arrangement as claimed in claim 17 wherein saidone pressure valve, which vents air from said reservoir, operates at apressure of about 25 psi.
 19. Hydraulic locking arrangement as claimedin claim 17 wherein said one pressure valve, which allows air into saidreservoir, operates at a negative pressure of about 25 psi. 20.Hydraulic locking arrangement as claimed in claim 3 wherein said airvalve arrangement has two air pressure valves, one of said pressurevalves operating to vent air in said reservoir at a predeterminedpressure and one of said air pressure valves operating to allow air intosaid reservoir at a predetermined negative pressure in said reservoir.